<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div class="box1"></div>
    <div id="app">
        <p>hello,node</p>
        <img src="../image/logo1.png" alt="">
        <!--这是一个注释-->
        <h1>标题1</h1>
        hello world!
    </div>
    <div class="box2">box2</div>
</body>
<script>
    let app = document.getElementById('app');
    let nextElement = app.nextElementSibling
    console.log(nextElement);
    let prevElement = app.previousElementSibling;
    console.log(prevElement);
    //第一个元素节点
    let firstElement = app.firstElementChild;
    console.log(firstElement);

</script>

</html>